import sys
input = sys.stdin.readline

N, K = map(int, input().rstrip().split())
A = []
for _ in range(K):
    a = list(map(str, input().rstrip().split()))
    A.append((int(a[0]), a[1]))
A.sort()

S = [0, 0, 0]
ans = []
for sa, c in A:
    a = int(sa)
    u = "RGB".index(c)
    now = S[u]
    others_max = max(S[(u+1)%3], S[(u-1)%3])
    su = sum(S)
    more = max(max((a+2)//3, others_max) - now, 0)
    if su + more <= a:
        S[u] += more
        for _ in range(more):
            ans.append(c)
    else:
        S = []
        break

if not S:
    print(-1)
else:
    while len(ans) < N:
        tmp = 10**18
        ind = -1
        for i in range(3):
            if S[i] < tmp:
                tmp = S[i]
                ind = i
        S[ind] += 1
        ans.append("RGB"[ind])
    print("".join(ans))